The present invention relates to a valve for use in abrasive fluid handling applications, which employs a plastic valve seat.
Machines and systems which are designed to carry fluids usually incorporate valves of various types to control the flow and pressure of fluids in the system. For example, spring-biased check valves are used to regulate the flow of fluid into a pump thereby maintaining the desired fluid flow, volume, or pressure within the pump. Similar valves are used to control the flow of fluids out of the pump.
The use of abrasive fluids under high pressure poses particular problems for the internal components of the fluid control valves. Latex paint can cause rapid wear of the valve seats in pumps used in airless paint spray systems, and of seats in valves used to control paint flow out of the spray gun. To minimize the resultant wear, tungsten carbide valve seats and poppets have been used. Tungsten carbide is, however, an expensive material. Also, its relative hardness means that the seat must be machined to very close tolerances so that it can be press-fit into the valve cartridge. Otherwise, it must be braised in place using heat. Also, a hard material such as tungsten carbide does not give as tight a seal as do softer materials which can deform to compensate for wear.
Valve seats made of plastic are well known and preferred because of their low cost and resilient sealing properties. In high pressure, abrasive environments such as that presented by an airless paint pump and spray gun, ultra-high molecular weight (UHMW) polyethylene is an ideal material, because it is both slick and long wearing, like tungsten carbide, while being much less expensive. Prior attempts at using UHMW polyethylene in paint control valves have not been truly successful, because of wear and extrusion problems. These problems have been primarily the result of valve designs that did not adequately support the seat, as UHMW polyethylene is not a structural material. The present invention solves these problems through a unique combination of design features which minimize the extrusion pressure on the seat and which transmit loads to surrounding structural components.